1. Field of the Invention
The present invention relates to a lead-free piezoelectric element and a multilayered piezoelectric element subjected to polarization. Also, the present invention relates to a liquid discharge head, a liquid discharge apparatus, an ultrasonic motor, an optical apparatus, an oscillatory apparatus, a dust removing apparatus, an image pick-up apparatus, and an electronic apparatus, which use the piezoelectric element or the multilayered piezoelectric element.
2. Description of the Related Art
Piezoelectric materials used for piezoelectric elements are generally ABO3-type perovskite-type metal oxides such as lead zirconate titanate (hereinafter referred to as “PZT”). However, PZT contains lead at an A-site of a perovskite skeleton. Therefore, the influence of a lead component on the environments is considered as a problem. In order to comply with the problem, a lead-free piezoelectric material and piezoelectric element using a perovskite-type metal oxide are proposed.
Barium titanate and derivatives thereof are known as piezoelectric materials composed of lead-free perovskite oxides. Japanese Patent No. 4039029 discloses a piezoelectric material and multilayered piezoelectric element in which A-sites of barium titanate are partially substituted by calcium to improve temperature stability of piezoelectric characteristics without decreasing the Curie point. The Curie points of these piezoelectric materials are the same as barium titanate, and thus there is still the problem of a low depolarization temperature at which piezoelectric characteristics disappear. The piezoelectric characteristics of piezoelectric elements undergoing polarization are generally degraded by depolarization at a temperature 10° C. to 20° C. lower than the Curie temperature. Also, the piezoelectric material disclosed in Japanese Patent No. 4039029 has the problem of low mechanical strength because the piezoelectric characteristics are improved by increasing the average grain diameter of crystal grains.
As another example, Japanese Patent Laid-Open No. 2009-215111 and “Journal of Applied Physics” 2011, Vol. 109, 054110-1 to 054110-6 disclose piezoelectric materials composed of barium titanate in which A-sites are partially substituted by calcium and B-sites are partially substituted by zirconium, thereby improving piezoelectric characteristics. The piezoelectric materials have a low Curie point of as low as 80° C. or less and have the problem of degrading the piezoelectric characteristics due to depolarization in a high-temperature environment in a vehicle in the summer. Also, the piezoelectric materials disclosed in Japanese Patent Laid-Open No. 2009-215111 have a low mechanical quality factor.
The present invention provides a lead-free piezoelectric element and a lead-free multilayered piezoelectric element which have good piezoelectric characteristics even in a high-temperature environment.
Also, the present invention provides a liquid discharge head, a liquid discharge apparatus, an ultrasonic motor, an optical apparatus, an oscillatory apparatus, a dust removing apparatus, an image-pickup apparatus, and an electronic apparatus, which use the piezoelectric element or the multilayered piezoelectric element.